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'[PIC]: 16F876 Timer 1 and SLEEP'
2002\09\30@105722 by Tim McDonough

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I have a project prototyped that requires the system to periodically take some readings and transmit them to another computer every 15 minutes. The exact interval isn't especially critical. A major consideration is that power consumption will be low since the device will run on AA batteries and we would like to replace them as infrequently as possible.

My design uses a main oscillator frequency of 4.0 MHz (crystal based) so I can get the timing I need during measurements and data transmission. The processing and transmission takes about 2 seconds. I'm using a 32 kHz crystal driving Timer 1 externally to very briefly wake up every 16 seconds, increment a software timer, and then go back to sleep until it's time for the 15 minute processing.

My question... What are people's experiences with data retention during sleep? Is it reliable? Can it be trusted?

So far my values appear to remain intact and I would prefer to not stash them in the on board EEPROM. I'm presently running two systems as a test, one leaves data in RAM, the other uses the EEPROM. After a few hours both are still in sync.

Tim

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2002\09\30@180010 by Jinx

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> My question... What are people's experiences with data retention
> during sleep? Is it reliable? Can it be trusted?

Yes, as long as you maintain the RAM retention voltage of > 1.5V

> So far my values appear to remain intact and I would prefer to not
> stash them in the on board EEPROM. I'm presently running two
> systems as a test, one leaves data in RAM, the other uses the
> EEPROM. After a few hours both are still in sync.

You've also got a heap of FLASH memory available. Nothing
wrong with using EEPROM or FLASH, which will protect your
data from power outages, but you have to watch the write-cycle
endurance. You should verify writes and cycle locations, as 15-
minute re-writes will use up the 1000-write endurance for a
single FLASH location quite quickly, much less so for the EEPROM
(100,000 ) or RAM

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